According to a Japanese Patent Application Laid-open publication H10 (1998)-138804, a powered seat sliding apparatus for a vehicle is exemplified as one of known powered seat sliding apparatus. As illustrated in FIGS. 1 and 2 for the present invention, the powered seat sliding apparatus cited above is provided with a motor equipped at a lower portion of a seat cushion and a pair of sliding mechanisms. Each sliding mechanism is provided as its main elements with a lower rail and an upper rail. The upper rail is movable relative to the lower rail in a lengthwise direction. A rotational speed of the motor is once reduced by a reduction mechanism and then transmitted to the sliding mechanisms. The reduced rotational speed of the motor is further reduced by a gear train, but the speed is increased again immediately in front of each sliding mechanism by the gears. Meantime, a rotational axis direction is switched via the gear train. A worm gear housed in the lower rail and supported by the upper rail of each sliding mechanism is rotated, in response to the transmitted motor rotation, wherein the movement of the upper rail of each sliding mechanism can be performed.
According to the powered seat sliding apparatus with the above-described structure, the worm gear supported by each upper rail is meshed with a slit train defined in a bottom surface of each lower rail (i.e. right and left lower rails). A torsion direction of the worm gear meshed with the slit train of the right lower rail is counter to a torsion direction of the other worm gear meshed with the slit train of the left lower rail, and the worm gears can provide a sliding force with the upper rails relative to the lower rails, when the worm gears apply thrust force by engaging with the slit train of each lower rails. According to the aforementioned structure, an inclined direction of the slit train defined in the bottom surface of the right lower rail is opposite to an inclined direction of the slit train defined in the bottom surface of the left lower rail. Therefore, the right and left lower rails are required to be exclusively applied for the right worm gear and the left worm gear, respectively. In this case, the number of requisite components may be unfavorably increased. Further, the feeding mechanism of the worm gear and the slit train inevitably have slight gaps or resiliency, therefore rattling may be caused with right and left feeding mechanisms.
Further, in the powered seat sliding apparatus with the above-described structure, the rotational force of the motor is transmitted to the gear train equipped to each sliding mechanism via an orthogonal shaft perpendicular to the lengthwise direction of the upper and lower rails. Alternatively, the transmitting of the rotational force can be carried out via a pair of rotary cables (i.e. right and left rotary cables) substituted for the orthogonal shaft. However, as far as a predetermined gear train is requisitely equipped to each sliding mechanism, the total number of components of the powered seat sliding apparatus may be increased so as to result in an increase of the manufacturing cost thereof. Further, unfavorable noise may occur due to the aforementioned structure.
Moreover, the motor, the reduction mechanism directly equipped to the motor, and the orthogonal shaft are all equipped to the seat cushion. In this configuration, the wheel gear displaced to transmit the rotational force from the seat cushion side to the worm gear disposed on the lower rail is large on account of a height of the seat cushion. As a result of it, lower efficiency of the power transmitting may occur through the decrease and increase of the rotational speed. Further, the gear trains equipped immediately in front of the sliding mechanisms may be sized-up so as to eventually result in the size-up of the powered seat sliding apparatus per se. Still further, the power transmitting is performed via the gear trains that have gaps therebetween, and an abrupt seat movement may occur when the seat moving operation is commenced. Even when the pair of rotary cables are substituted for the orthogonal shaft, the above-described drawbacks may still occur as far as the gear trains are equipped immediately in front of the sliding mechanisms.
Further, another powered seat sliding apparatus is disclosed in a Japanese Patent Application Laid-open publication H10 (1998)-968. The powered seat sliding apparatus is provided with a pair of sliding mechanisms. Each sliding mechanism is provided at its main elements with a lower rail and an upper rail. The lower rail is physically held by the upper rail. A lateral width of each sliding mechanism is determined by the width of the upper rail.
A worm gear is disposed in an inner place defined by the upper rail and the lower rail and is supportably hung on a ceiling of the upper rail. More particularly, the worm gear is supported by a housing portion hung from an upper housing portion corresponding to the ceiling of the upper rail. Therefore, a moving force can be transmitted from the worm gear to the upper rail.
According to the sliding apparatus with the above-described structure, the width of the sliding mechanism may be increased. A housing supporting the worm gear is fixed to the upper rail through a ceiling bore of the upper rail. Therefore, when a large load is applied, a twist stress may be applied from the worm gear to a fixed portion with the worm gear. Therefore, the housing is required to have large size for assuring the strength for the stress. Still further, the slit trains formed at tip end portions of the lower rail are processed by cutting because the upper and lower rails are substantially thick and complicated cross-sections which should be formed by light metals extrusion process. Therefore, the manufacturing cost of the lower rail may be raised up.
Accordingly, it is still susceptible of certain improvements with respect to providing an improved powered seat sliding apparatus which can be manufactured with the less number of requisite components at a lower manufacturing cost and can restrain the noise occurrence. Further, the improved powered seat sliding apparatus is required to restrain rattling of both feeding mechanisms and to restrain the abrupt seat movement when the seat moving operation is commenced.